salt: minion upgrade occasionally fails with The renderer "yaml_jinja" is not available

Description of Issue/Question

Upgrading salt-minion from 2016.11.2 to 2018.3.2 have always been failing a bit randomly (~50%), with high probability the minion entering a running but non-responding state, logging

2018-09-28 18:17:23,128 [salt.utils.parsers                                   ][WARNING ][165127] Minion received a SIGTERM. Exiting.
2018-09-28 18:17:31,900 [salt.template                                                  ][ERROR   ][172291] The renderer "yaml_jinja" is not available
2018-09-28 18:17:31,900 [salt.loader                                                    ][CRITICAL][172291] The renderer yaml_jinja is unavailable, this error is often because the needed software is unavailable
2018-09-28 18:17:31,900 [salt.minion                                                    ][WARNING ][172291] The minion function caused an exception

Simply restarting the minion resolves the problem (and magically making yaml_jinja present again). (But the restart takes a visibly longer time, like 30 seconds.) I have tried to install python3 jinja and yaml before upgrading minion (it’s just hand-waving since the package does that anyway) but didn’t help.

(Tried to search issues, found nothing relevant.)

Setup

Debian jessie and stretch mixed; master is either 2016.11 or 2018.3, both fails the same. (2018 is from the official salt repo, 2016 is from Debian repo.)

Multimaster, but I don’t think it’s relevant. (As a sidenote upgrade “always” fail when ipv6:True and the masters only have ipv4 addresses. It’s been working before but I’m not sure whether it’s a bug or a feature.)

Minion config:

/etc/salt/minion.d/proxy.conf:proxy_host: proxy.x.y
/etc/salt/minion.d/proxy.conf:proxy_port: 3128
/etc/salt/minion.d/_schedule.conf:schedule:
/etc/salt/minion.d/_schedule.conf:  __mine_interval: {enabled: true, function: mine.update, jid_include: true, maxrunning: 2,
/etc/salt/minion.d/_schedule.conf:    minutes: 60, return_job: false}
/etc/salt/minion.d/l.conf:master: 
/etc/salt/minion.d/l.conf:  - salt2.x.y
/etc/salt/minion.d/l.conf:  - salt1.x.y
/etc/salt/minion.d/l.conf:master_tries: -1
/etc/salt/minion.d/l.conf:#damnyou# ipv6:true 
/etc/salt/minion.d/l.conf:grains:
/etc/salt/minion.d/l.conf:  roles:
/etc/salt/minion.d/l.conf:    - default_config
/etc/salt/minion.d/l.conf:    - ct
/etc/salt/minion.d/l.conf:    - no_default_users
/etc/salt/minion.d/l.conf:  cluster: hackworth

Steps to Reproduce Issue

{% if pillar['salt-official-latest'] is defined %}
update-salt-official-latest:
  pkg.latest:
    - pkgs:
      - salt-minion
      - salt-common
    - cache_valid_time: 600
    - install_recommends: True
    - only_upgrade: True
    - require:
      - pkg: salt-required-other-pkgs

restart-when-updated-official:
  service.running:
    - name: salt-minion
    - watch: 
      - pkg: update-salt-official-latest
{% endif %}   

# salt require these
salt-required-other-pkgs:
  pkg.latest:
    - pkgs:
{% if pillar['salt-official-latest'] is defined %}
      - python3-jinja2
      - python3-yaml
      - python3-apt
{% else %}
      - python-apt
{% endif %}      

Versions Report

Source:

Salt Version:
           Salt: 2016.11.2
 
Dependency Versions:
           cffi: Not Installed
       cherrypy: Not Installed
       dateutil: 2.5.3
          gitdb: Not Installed
      gitpython: Not Installed
          ioflo: Not Installed
         Jinja2: 2.7.3
        libgit2: Not Installed
        libnacl: Not Installed
       M2Crypto: Not Installed
           Mako: 1.0.0
   msgpack-pure: Not Installed
 msgpack-python: 0.4.2
   mysql-python: Not Installed
      pycparser: Not Installed
       pycrypto: 2.6.1
         pygit2: Not Installed
         Python: 2.7.9 (default, Jun 29 2016, 13:08:31)
   python-gnupg: Not Installed
         PyYAML: 3.11
          PyZMQ: 14.4.0
           RAET: Not Installed
          smmap: Not Installed
        timelib: Not Installed
        Tornado: 4.4.1
            ZMQ: 4.0.5
 
System Versions:
           dist: debian 8.9 
        machine: x86_64
        release: 4.4.35-1-pve
         system: Linux
        version: debian 8.9 

Target:

Salt Version:
           Salt: 2018.3.2
 
Dependency Versions:
           cffi: Not Installed
       cherrypy: Not Installed
       dateutil: 2.5.3
      docker-py: Not Installed
          gitdb: Not Installed
      gitpython: Not Installed
          ioflo: Not Installed
         Jinja2: 2.9.4
        libgit2: Not Installed
        libnacl: Not Installed
       M2Crypto: Not Installed
           Mako: Not Installed
   msgpack-pure: Not Installed
 msgpack-python: 0.4.8
   mysql-python: Not Installed
      pycparser: Not Installed
       pycrypto: 2.6.1
   pycryptodome: Not Installed
         pygit2: Not Installed
         Python: 3.5.3 (default, Jan 19 2017, 14:11:04)
   python-gnupg: Not Installed
         PyYAML: 3.12
          PyZMQ: 16.0.2
           RAET: Not Installed
          smmap: Not Installed
        timelib: Not Installed
        Tornado: 4.4.3
            ZMQ: 4.2.1
 
System Versions:
           dist: debian 9.3 
         locale: UTF-8
        machine: x86_64
        release: 4.4.35-1-pve
         system: Linux
        version: debian 9.3